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Optical transmission
Published in John P. Dakin, Robert G. W. Brown, Handbook of Optoelectronics, 2017
Michel Joindot, Michel Digonnet
Raman amplification relies on SRS, a nonlinear optical process that causes power transfer between an optical pump and a signal (see “Stimulated Raman Scattering” section). One of the greatest strengths of Raman amplification is that it can supply gain at any wavelength provided a suitable pump source is available. Since the Raman shift of silica is typically 13 THz, to obtain a gain peak at 1530 nm the pump wavelength must be ~1430 nm. With such a pump, gain will be available from about 1490–1546 nm. The Raman gain cross section of silica is unfortunately relatively small, so the power requirement is much higher than for an EDFA, but Raman fiber amplifiers present several important benefits that somewhat mitigate this disadvantages, including the flexibility of pump wavelength selection, the availability of gain anywhere where pump is available, and the fact that the gain medium is the transmission fiber itself.
Nonlinearity in Guided Wave Devices
Published in Le Nguyen Binh, Guided Wave Photonics, 2016
where P0I0Aeff is the pump power. One of the most important parameters for Raman amplification in any application is the Raman effective gain coefficient, which is defined as geffR=gR/Aeff where gR is the Raman gain coefficient. The effective Raman gain coefficient depends not only on the Raman gain coefficient itself but also on the effective area of the fiber. Hence it leads to the significance of designing a fiber with a small effective area in order to achieve high gain. In addition, flattening the Raman gain coefficient as much as possible is also a desirable need. DCF fiber offers excellent gain medium for discrete Raman amplifiers [78] which have already been started to be widely deployed in the long-haul transmission systems.
Ultra-fast optical switch with reconfigurable wavelength reuse functionality for dynamic flexible spectrum networks
Published in Journal of Modern Optics, 2019
G. M. Isoe, D. Kiboi. Boiyo, E. K. Rotich, T. B. Gibbon
To maintain a high quality of signal of the trans-reflected channel over the entire transmission fibre, forward Raman amplification was adopted. Results in Figure 5(b). For demonstration purpose, a free running unmodulated VCSEL channel was considered for this measurement. The central emission wavelength of the VCSEL was maintained at 1550.64 nm by adjusting its bias current to 5.68 mA. A 25.36, 50.6, 75.3 and 100.8 km of SMF-REACH fibres was considered. A forward and backward Raman pumping techniques were also considered respectively. Here, forward pumping is used to imply when the Raman pump is coupled with the transmitted signal from the transmitter end therefore the two are allowed to propagate in the same direction, while backward pumping imply a case where the Raman pump is placed on the receiver end to amplify the signal before its recovery, therefore the signal propagates in a direction opposite to that of the transmitted signal. As shown in Figure 5(b), forward Raman amplification was noted to have a higher gain than backward Raman amplification, therefore justifying the adoption of forward Raman pumping technique in this work.
Integrated extended reach VCSEL interconnect with 8.5 Gbps data modulated forward Raman pump signals
Published in Journal of Modern Optics, 2019
G. M. Isoe, D. Kiboi Boiyo, E. K. Rotich, D. M. Osiemo, T. B. Gibbon
Raman amplification is a key developmental technology to improve the optical fibre network performance with improved OSNR. Other than high distributed gain, Raman systems are compatible with a wideband transmission window (up to 100 nm) and can support different advanced modulation formats. In this work, we experimentally present the first reported integrated cross modulated forward pumped distributed Raman amplifier (DRA) with low-cost, power-efficient vertical cavity surface emitting lasers (VCSELs). In our previous work (9), we demonstrated a low-cost energy efficient technique for maximizing carrier spectral efficiency and extending transmission reach through combined adoption of VCSELs, four-level pulse amplitude modulation (4-PAM), dense wavelength division multiplexing and Raman amplification. Here, we experimentally demonstrate a technique to maximize the network efficiency by adopting an 8.5 Gbps modulated forward Raman pump to simultaneously offer distributed Raman amplification over a VCSEL channel as well as the transfer of data signals.